1. Field of the Invention
The present invention relates to an audio processing system and method capable of preventing noise.
2. Related Art
Currently, a hybrid set-top box which receives at least two broadcast signals, such as a satellite signal, a terrestrial signal, and so forth, and which outputs one broadcast signal to a television (TV) or a personal computer (PC) at a user's command, is under development. The hybrid set-top box is an example of a large class of mainstream consumer electronic devices employing an audio processing system which selects one of a plurality of input audio signals and outputs the audio signal through an audio output device, e.g., a speaker.
An audio processing system comprises a plurality of input units, a selector, and an amplifier.
The input units are connected to audio equipment, e.g., a digital versatile disc (DVD) player, a stereo system, etc., and they output audio signals received from the audio equipment to the selector.
According to a selection signal input from a remote controller or a selection button manipulated by a user, the selector selects one of the audio signals inputted through the input units, and outputs it to the amplifier.
The amplifier amplifies the voltage level of the audio signal received from the selector by a predetermined ratio, and outputs it to a digital terminal, such as a TV or PC.
However, when the selector selects a second audio signal received from a second input unit at the user's command while the amplifier outputs a first audio signal received from a first input unit, pop noise is generated due to a difference in voltage level between the first and second audio signals.
In general, the audio processing system is designed in such a manner that the voltage level difference between audio signals inputted to the input units should range from 0 V to a value between about 0.2 V and 0.5 V.
Even if the voltage level difference between audio signals received from the input units is not large, it is amplified while passing through the amplifier, and thus pop noise is generated.
A different type of audio processing system also comprises a plurality of input units, a selector, and a plurality of amplifiers.
The amplifiers amplify each audio signal inputted through the input units by a predetermined ratio, and then the selector selects one of the audio signals at a user's command and outputs it to a digital terminal.
However, the amplifiers corresponding to the input units of the audio processing system are quite costly.
In addition, when the selector switches from an amplified first audio signal to an amplified second audio signal at the user's command, pop noise is generated due to a voltage level difference between the amplified audio signals.
Meanwhile, a one-to-one connection method has been used in order to prevent pop noise in an audio processing system. The one-to-one connection method involves removal of the selector which serves as a switch operating at a user's command, separate amplification of each audio signal input through at least one input by the amplifiers, and output of each amplified audio signal to a digital terminal.
However, the one-to-one connection method is quite costly since the audio signals separately amplified by each amplifier, must be sent to a digital terminal through separate lines. Also, the one-to-one connection method requires that the user manually connect the digital terminals to the amplifiers.